This invention is a deposition head which is useful in the process which is termed directed light fabrication (DLF) or the DLF process. Directed light fabrication may be used to produce articles of any material which is obtainable in the form of a powder, but its primary use is expected to be production of metal articles.
Metal objects are currently produced by thermomechanical processes which include casting, rolling, stamping, forging, extrusion, machining, and joining operations. Multiple steps are required to produce a finished article. These conventional operations often require the use of heavy equipment and molds, tools, and dies. For example, a typical process sequence required to form a small cylindrical pressure vessel might include casting an ingot, heat treating and working the casting to homogenize it by forging or extrusion or both, then machining a hollow cylinder and, separately, end caps from the worked ingot and, finally, welding the end caps to the cylinder. The DLF process provides a method for forming such an article in a single operation and using less equipment. An article formed by laser deposition is relatively free of internal stresses in comparison to an article formed by welding one or more components together. Also, joining components by means of welding requires equipment just for the single step of joining and time to set up the equipment to do the job.
Conventional production methods are subtractive in nature in that material is cut away from a starting block of material to produce a more complex shape. Subtractive machining methods are deficient in many respects. Large portions of the starting material are reduced to waste in the form of cuttings. These methods produce waste materials, such as metal cuttings, oils, and solvents, which must be further processed for purposes of reuse or disposal. The articles produced are contaminated with cutting fluids and metal chips. They require cutting tools which wear and must be periodically reconditioned and ultimately replaced. Fixtures for use in manufacturing must be designed, fabricated, and manipulated during production. When a part is unusual in shape or has internal features, machining is more difficult. Choosing the machining operations to be used and the sequence of operations requires a high degree of experience. A number of different machines are needed to provide capability to perform the variety of operations which are often required to produce a single article. Sophisticated machine tools require a significant capital investment and occupy a good deal of space. Use of DLF in place of subtractive machining provides solutions to these problems and disadvantages. The DLF process may be characterized as additive in nature. The raw material which does not become part of an article is easily collected and re-used without processing. There is no need to dispose of waste liquids and metal cuttings and the articles produced are not contaminated by these materials. Fixtures and cutting tools are not required. All work needed to produce an article is accomplished using a computer workstation and a single production station. Also, this invention can be used to rapidly provide production tooling after article design is frozen.
Another difficulty with conventional machining techniques is that many objects must be produced by machining a number of parts and then joining them together. Producing parts separately and joining them requires close-tolerance machining of matching parts, provision of fastening means, such as threaded connections, and welding together of components. These operations involve a significant portion of the cost of producing an article, as they require time for design and production as well as apparatus for performing them.
The process of designing an article for volume production often consumes a good deal of time. Much of this time is spent in producing prototypes. Prototyping may require specialized apparatus and services which are not available in-house. Molds, tools, and dies are particularly difficult to obtain rapidly. Once a prototype is made, it is often necessary to make changes in the design and make another prototype. The present invention provides a method for rapid prototyping. As commonly used today, rapid prototyping refers simply to making a pattern or non-functional part. A non-functional article allows fit and form to be tested. It is considerably more difficult and time-consuming to make a prototype to test function, that is, which has the mechanical properties needed to test the article in its intended use. The DLF process is capable of producing a true rapid prototype, which can be used in a service test to investigate stresses, strains, fracture properties, and wear properties. After testing, the design of the article may be changed and another true prototype made and tested. This rapid reiteration provides an ability to optimize a design in a short period of time.
An article made by the DLF process has annealed properties, that is, its microstructure and metallurgical properties are similar to articles which have been annealed. If the material of a DLF article is heat-treatable, the properties of the article, such as strength, ductility, fracture toughness, and corrosion resistance, can be modified by means of heat treatment. An article formed by a conventional cold working process of a material having a large strain-hardening coefficient (such as austenitic stainless steel) will have relatively high strength compared to a DLF-formed article. Examples of cold working processes are forging and extrusion. If, however, a cold-formed article is subjected to the heat of welding, its strength will be reduced to that of annealed articles. Thus, DLF is an attractive alternative to fabrication by subtractive machining and welding, but cannot be substituted for processes in which a near net shape article is fabricated by cold-forming without welding and the high strength of cold-forming is required.
Following are descriptions of background patents.
U.S. Pat. No. 4,724,299 teaches a nozzle for cladding of an object using metal powder melted by a laser beam.
U.S. Pat. No. 5,111,021 deals with adding material to a surface using a laser beam and metal powder and discloses a nozzle for doing so.
U.S. Pat. No. 4,743,733 teaches repair of an article by directing a laser beam and a stream of metal powder to a region of the article which requires repair.
U.S. Pat. No. 4,323,756 teaches a method for producing metallic articles from metal powders and substrates which become part of the articles. A focused energy beam is used to create a molten pool on a substrate and metal powder is supplied to a point outside of the area at which the beam impinges upon the substrate. Movement of the substrate then carries the powder into the beam and molten pool, where it melts and mixes with the melted substrate material.